1. Field of the Invention.
The present invention relates to a method and apparatus for processing reaction resin that is harden with ultra-violet (UV) light.
2. Description of Related Art.
Radiation hardenable reaction resins are frequently preferred over thermally hardenable reaction resins because the former harden substantially faster at low temperatures and have a nearly unlimited use life.
Radiation hardenable reaction resins are commonly irradiated after applying the reaction resin as disclosed, for example, in European Patent Application No. 0 094 915 A3. For example, UV hardening varnishes are irradiated over the whole surface after the varnishing process. Compounds to cover the electronic circuitry are likewise irradiated over the whole surface after the covering operation or exposed by scanning with focused radiation sources often comprising short flashes.
More recent attempts to cover small electronic components, such as LEDs, with UV-hardening compounds assume that the exposure process occurs after the casting. The hardening effectively occurs in the mold and optionally through the latter. The same process is also used for encapsulating passive components such as foil capacitors.
The foregoing applications have the disadvantage that the irradiation must be performed on the "finished" object, i.e., the place of the irradiation is fixed by the device to be coated or encapsulated.
The irradiation is typically performed with shortwave electromagnetic radiation or electron radiation, i.e., with radiation which is easy to mask. Therefore, masking by undercutting the device to be coated is an important problem.
The irradiation of a finished object triggers a chemical reaction through absorption of the radiation. The penetration of the radiation into lower layers is diminished by absorbed in upper layers. Further, the decomposition products produced by these chemical reactions also absorb UV radiation so that even less radiation is available for hardening deeper layers. It is therefore practically impossible to homogeneously activate thick structures with radiation since, in practice, no resin matrix is perfectly transparent to UV radiation.
European Patent Application No. 0,094,915 discloses the preparation of storable activated preliminary stages from UV-reactive resins by irradiation followed by heat hardening. The preliminary stage is generated directly on a substrate. However, this method suffers the same disadvantages as thicker layer structures due to shading.